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 <html lang="en">
 <head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
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    <script>
      var a = 5;

      var b = ++a; // b = 6

      var a = 5;

      var b = a++ // b = 5
    </script>
 </body>
 </html>